Straw Detectors Research Articles

Mapping the large area straw detectors of the COMPASS experiment with X-rays

In the COMPASS experiment at CERN, large straw drift tube detectors are used for large-angle tracking. To minimize the total areal density, a self supporting structure of thin-walled plastic tubes was chosen and, hence, a loss in mechanical precision was accepted. A complete mapping of the anode wire coordinate grid was required. An X-ray apparatus using a charge-coupled device (CCD) as imaging detector was built to investigate the mechanical properties and to calibrate (offline) the wire positions. Deviations of typically 200-400 /spl mu/m from the nominal positions, defined by equal spacing, are found across the detector area of 8 m/sup 2/. With a calibration method based on high-resolution CCD imaging and pattern recognition algorithms, the absolute wire coordinates are determined with an accuracy better than 30 /spl mu/m across the whole detector area. Temperature effects are clearly seen. Their inhomogenity limits the achievable accuracy to about 50 /spl mu/m under realistic experimental conditions, which is sufficient in view of the intrinsic straw resolution of 200 /spl mu/m for minimum ionizing particles. The offline calibration was checked with particle tracks in the experimental setup, running COMPASS with 160 GeV/c muons. Tracks reconstructed with other detectors that cover a central angular range were used for this comparison. Good agreement is found between these in situ measurements and the X-ray calibration.

High sensitivity, low cost PET using lead-walled straw detectors

Positron Emission Tomography (PET) is a highly sensitive imaging modality particularly useful in oncology imaging. Unfortunately, the high cost of crystal detectors and limited axial field of view of current systems pose major limitations in this clinical application. A novel technology for detection of 511 keV photons for coincidence PET imaging is proposed based on lead walled straw tubes (LWS). Such detector tubes have been produced and investigated both experimentally and with Monte Carlo techniques. Initial results of detector efficiency versus lead wall thickness, time resolution, and longitudinal spatial resolution are presented. A technique of modular fabrication is also described. It is proposed that a low cost PET camera can be designed using the basic LWS in close packed modular arrays. Such a camera can provide full three-dimensional, high resolution PET with very large axial acceptance and therefore very high sensitivity.

Signal propagation in straw tubes with resistive cathode

The analysis presented in this paper is part of the research performed by the authors for the COMPASS experiment at CERN. We have developed a theoretical model of the signal transmission in a straw tube. In contrast to commonly used simplified models, our approach takes into account the energy losses in the cathode resistance. This model allows determination of the main electrical parameters, such as characteristic impedance and signal attenuation, as well as a detailed simulation of the pulse shape dependent on the point of the charge injection. Simulation results have been compared with the results of experimental measurements of different types of the straw detectors.